Complement modulation in the retinal pigment epithelium rescues photoreceptor degeneration in a mouse model of Stargardt disease

Abstract

Recessive Stargardt macular degeneration (STGD1) is caused by mutations in the gene for the ABCA4 transporter in photoreceptor outer segments. STGD1 patients and Abca4−/− (STGD1) mice exhibit buildup of bisretinoid-containing lipofuscin pigments in the retinal pigment epithelium (RPE), increased oxidative stress, augmented complement activation and slow degeneration of photoreceptors. A reduction in complement negative regulatory proteins (CRPs), possibly owing to bisretinoid accumulation, may be responsible for the increased complement activation seen on the RPE of STGD1 mice. CRPs prevent attack on host cells by the complement system, and complement receptor 1-like protein y (CRRY) is an important CRP in mice. Here we attempted to rescue the phenotype in STGD1 mice by increasing expression of CRRY in the RPE using a gene therapy approach. We injected recombinant adeno-associated virus containing the CRRY coding sequence (AAV-CRRY) into the subretinal space of 4-wk-old Abca4 −/− mice. This resulted in sustained, several-fold increased expression of CRRY in the RPE, which significantly reduced the complement factors C3/C3b in the RPE. Unexpectedly, AAV-CRRYtreated STGD1 mice also showed reduced accumulation of bisretinoids compared with sham-injected STGD1 control mice. Furthermore, we observed slower photoreceptor degeneration and increased visual chromophore in 1-y-old AAV-CRRY-treated STGD1 mice. Rescue of the STGD1 phenotype by AAV-CRRY gene therapy suggests that complement attack on the RPE is an important etiologic factor in STGD1. Modulation of the complement system by locally increasing CRP expression using targeted gene therapy represents a potential treatment strategy for STGD1 and other retinopathies associated with complement dysregulation.recessive Stargardt macular degeneration | complement system | retinal pigment epithelium | bisretinoids | gene therapy R ecessive Stargardt macular degeneration (STGD1) is a blinding disease of children and young adults caused by mutations in the ATP binding cassette subfamily A member 4 (ABCA4) gene (1, 2). The pathological hallmark of STGD1 is deposition of autofluorescent lipofuscin in the retinal pigment epithelium (RPE), which precedes photoreceptor degeneration (3, 4). The exact mechanism of how RPE lipofuscin accumulation disrupts overall RPE performance is poorly understood. The RPE fulfills several photoreceptor support tasks, including phagocytosis of distal outer segments (OS) and processing of visual retinoids (5-8). In addition, the RPE plays a major role in controlling the ocular immune response through expression of various complement negative regulatory proteins (CRPs) (9). For these reasons, photoreceptors are critically dependent on a healthy RPE for continued viability.The ABCA4 transporter clears retinaldehyde released by photobleached rhodopsin and cone-opsins from OS discs in the form of N-retinylidene phosphatidylethanolamine (N-ret-PE) (10). As a result, mice lacking ABCA4 accumulate retinaldehyde and N-ret-PE in their OS after light exposu...

Fundus autofluorescence, spectral‐domain optical coherence tomography, and histology correlations in a Stargardt disease mouse model

“…Seven days after BLI, the eyes from the Abca4 −/− mice were enucleated, immediately snap‐frozen and stored at −80°C for further processing. All the tissue preparation was made under dim red light and bisretinoids were extracted from the whole eyes and analyzed by HPLC following published methods . Data were presented as picomoles per eye for A2E and milli‐absorbance (mAU) per eye for the other bisretinoids: A2PE, dihydro‐A2PE (A2PE‐H 2 ), and all‐trans‐RAL‐dimer PE conjugates (at‐RAL dimer‐PE).…”

Lipofuscin Accumulation into and Clearance from Retinal Pigment Epithelium Lysosomes: Physiopathology and Emerging Therapeutics

“…Alternatively, LB-photooxidation could be damaging through its propensity to activate the complement system [62]. In support of this idea, there is a histologic evidence of complement deposition in drusen of retinas with AMD [63] and animal studies show that overexpression of inhibitors of complement protects retinas of mice with elevated LB content [64]. Furthermore, genetic polymorphism in genes encoding complement factor H (CFH), CFB component C2, CFI, and complement components 2, 3 and 7 has been associated with elevated risk for LB-driven retina disease.…”

New GABA modulators protect photoreceptor cells from light‐induced degeneration in mouse models

“…There have been substantial efforts to develop effective therapeutics for preventing nonexudative retinal degenerative diseases. These include sequestration of toxic all ‐trans retinal by primary amines (43, 57); increasing clearance of retinoid metabolites with visual cycle inhibitors (10, 11); modulating GPCR signaling (54); and the use of neuroprotective agents (58), antioxidants (6), and gene therapy (59, 60). Many of these approaches have been successful in mice.…”